The objective of the proposed study is to compare B-lymphocyte function in persons of different ages. In addition, the contribution of altered monocyte function to the impaired immune response will be studied: 1. Application of the reverse PFC assay for assessment of the B-lymphocyte function in humans of different ages. 2. To continue the studies on the B-lymphocyte function of aged humans by using both rabbit anti-human micro-chain and allogeneic T-cell factor. 3. To continue the studies on the regulatory mechanism for the generation of suppressor cells and helper cell in allogeneic MLC. 4. The measurement of total immunoglobulins secreted in the culture of B-lymphocytes activated by polyclonal mitogens. 5. Development of the technique for cloning B-cells from both young and aged humans and the establishment of continuous B-cell lines.